Newsmedia doesn’t appear to understand the federal system.
A special agent can only arrest a person if there is a warrant or if a crime is committed in his presence.
Once they ID’d the person here, they US Attorney had to be called in. Take him into custody, bring him to federal court, and charge him.
And people don't understand police scanners either, especially those who attempt to use them as sources for confirming information. They aren't official, so information people hear from them shouldn't be considered as confirmed.